It is known to make a window covering from a plurality of diverse panels which can be moved selectively in front of a window to control the light level or temperature or air flow in the room. Such window coverings are disclosed in U.S. Pat. Nos. 3,186,473 in the name of D. E. Meyers et al.; 3,236,290 in the name of Lueder; 4,766,941 in the name of Sloop et al.; 4,813,198 in the name of Johnston et al.; and 4,815,515 in the name of Lee et al. Devices of this general type are also sold by Mecho Shade Corporation of Long Island City, N.Y. and Draper Shade & Screen Corp., Inc.
In U.S. Pat. No. 3,186,473, an electric motor mounted adjacent the lower roller causes a panel to wind from an upper roller onto an lower roller. The panels are rewound onto the upper roller by a mechanical crank on the upper roller. The exterior motor takes up space alongside the window and is in a position at which persons near the lower roller are exposed to the motor wiring. Further, it is awkward to have to mechanically rewind the upper roller to move the panel upward.
In U.S. Pat. No. 3,236,290, a mechanical crank is connected to both upper and lower rollers and rotates them simultaneously. The crank may also be motor operated by a control adapted to move a light controlling and/or thermal controlling panel in position to maintain a constant light level (or thermal level) in a room. A torsion spring in the crank arm maintains a stretching force on the panel suspended between the rollers. The torsion spring is external of the rollers and the crank arm or motor are also external of the rollers and the wiring is at the windowsill level.
U.S. Pat. No. 4,766,941 employs electric motors and torsion springs in both upper and lower rollers, with the motors secured to the support bracket independently of the rollers. Thus noise reduction is impaired and wiring is located at windowsill level.
U.S. Pat. No. 4,813,198 employs an elongated panel between an upper and lower roller. The upper roller has a short helical return spring adjacent its end and a mechanical crank or motor for rotating the lower roller. Again, all parts are external of the rollers, the wiring for a motor is at the lower roller, and the shade is hard to install.
U.S. Pat. No. 4,815,515 shows a motor-driven upper roller with the motor disposed external of and adjacent to the upper roller, and a spiral spring (with coils wound atop one another) mounted adjacent to and externally of the lower roller.
The system sold by Mecho Shade Co. employs a freely suspended shade with a motor driven gear drive which is secured to an end bracket which is exterior to and mounted independently of the hollow roller tube. End stops are employed to stop the motor rotation between two end positions.
Systems sold by Draper include an overhead unit in which the cover is in a horizontal plane with a relatively short panel and a freely vertically suspended panel with a drive motor fixed to an exterior bracket.